Serialize metadata

pkg/compiler/lib/src/js_backend/backend.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 3058 matching lines @@
     return transformed;
   }
 }
 
 /// Records that [constant] is used by the element behind [registry].
 class Dependency {
   final ConstantValue constant;
   final Element annotatedElement;
 
   const Dependency(this.constant, this.annotatedElement);
+
+  String toString() => '$annotatedElement:${constant.toStructuredText()}';
 }
 
 class JavaScriptImpactStrategy extends ImpactStrategy {
   final Resolution resolution;
   final DumpInfoTask dumpInfoTask;
   final bool supportDeferredLoad;
   final bool supportDumpInfo;
   final bool supportSerialization;
 
   JavaScriptImpactStrategy(this.resolution, this.dumpInfoTask,
@@ skipping 25 matching lines @@
 
   @override
   void onImpactUsed(ImpactUseCase impactUse) {
     if (impactUse == DeferredLoadTask.IMPACT_USE && !supportSerialization) {
       // TODO(johnniwinther): Allow emptying when serialization has been
       // performed.
       resolution.emptyCache();
     }
   }
 }